dtrace/arm64: Fix copyout and copyoutstr

[freebsd_dev.thsi.be]

Summary

Calling dtrace_copy and dtrace_copystr with the kaddr and uaddr
arguments inversed does not work with PAN. Rename them
dtrace_copyin_pan and dtrace_copyinstr_pan, respectively, and
implement dtrace_copyout_pan and dtrace_copyoutstr_pan.

Avoid excessive faulting by checkin DTrace's CPU flags. Implement the
trick from OpenSolaris/Illumos of only checking the flags when
crossing into a new page, altough more effectively by examining the
vaddr instead of the count.

[freebsd_dev.thsi.be]

sys/cddl/contrib/opensolaris/uts/common/sys/dtrace_impl.h

1306

I'd like to take care of the armv6 case later. It alsos need the copy -> copyin rename and a new copyout versions. i'd like to use the same names, so dunno maybe it is better to use something else than _pan, e.g. _unpriv ?

[freebsd_dev.thsi.be]

For the record, the current broken behavior can be tested like this:

echo "Hello world!" > greetings
cat <<"EOT" > copyout.d
syscall::read:entry
/pid == $target/
{
	this->ubuf = arg1;
}

syscall::read:return
/pid == $target/
{
	self->kbuf = alloca(10);
	copyoutstr("Ciao ", this->ubuf, 5);
	copyinto(this->ubuf, 10, self->kbuf);
	copyout((void*)((uint64_t)self->kbuf+5), this->ubuf, 5);
}
EOT
dtrace -w -s copyout.d -c "cat greetings"

correct output:

dtrace: script 'copyout.d' matched 4 probes
dtrace: allowing destructive actions
 worl world!
dtrace: pid 5724 has exited